The invention is based on a fuel injection pump for Diesel engines having a pump cylinder, a pump piston in the cylinder, and the pump piston being provided with at least one control recess. The pump piston is adapted to be reciprocated by a cam means and a cooperating spring means, with a control means arranged to encircle the pump piston and with the control means associated with a hydraulic adjusting means. The control means is arranged to cooperate with the control recess for varying the injection quantity and thereby the instant of injection. An injection pump having a pump cylinder, a pump piston dipping into this pump cylinder, and a hydraulic adjusting device for the instant of injection is known from U.S. Pat. No. 2,313,264. The adjusting device has an elastic bellows inside a chamber, the closed end of the bellows being movable, a spring which expands the bellows, a rack connected with the end of the bellows, a gear wheel meshing with this rack having an internal thread, and a stop sheath secured against rotation, the outer thread of which is threaded into the gear wheel. The stop sheath has a collar which determines the outset position of the pump piston. The pump piston is lifted toward this collar by means of a spring. An adjusting mechanism having a rack and a gear wheel is conventional, but expensive. In order to attain high adjustment precision, the rack, the gear wheel and the stop sheath must be supported with as little play as possible and must mesh with one another without play. This makes the manufacture of such elements expensive. A further disadvantage of this injection pump is that its pump piston is driven by a control cam via a hydraulic push rod which compensates for play. In addition, a further pump must also be provided which supplies the push rod with pressure fluid in the form of oil.
In an injection pump known from the unexamined Japanese patent application No. 131562/80 or proposed in the British application No. 2076074A, made public in the interval since the priority date, the instant of injection is fixed by means of adjusting the height or level of a control sleeve, which sealingly surrounds the pump piston, which moves vertically up and down with a constant stroke height, and has at least one control recess directed toward the pump piston, the recess being overtaken by a control opening disposed in the pump piston. The control sleeve is lifted or lowered via an adjusting shaft, the pivoting shaft of which is directed transversely relative to the longitudinal axis of the pump piston, and via an adjusting tang which is inserted into one end of the adjusting shaft and engages the control sleeve. The adjusting shaft protrudes out of the housing of the injection pump and carries an adjusting lever. The adjusting levers for a plurality of sleeves may be pivoted in common via tangs, for instance by means of a sliding rod. Injection pumps known from British Pat. No. 442,475 and European Pat. No. EP-A1-0027790 also have control sleeves which surround the pump pistons and are adjustable in their stroke directions. The adjustment is again effected by means of pivotable shafts which are carried outside the housing of the pump. The expensive hydraulic injection pump system according to U.S. Pat. No. 2,313,264 avoids the disadvantages of the mechanical adjustment of control sleeves in common with one another. Accordingly, the object of creating an improved and less expensive injection pump having a hydraulic adjustment of the instant of injection presented itself.